The present invention relates to a semiconductor device; and, more particularly, to a semiconductor device having a ferroelectric capacitor for use in a memory cell and a method for the manufacture thereof.
As is well known, a dynamic random access memory (DRAM) having a memory cell comprised of a transistor and a capacitor has paved the way to a higher degree of integration mainly by down-sizing through micronization. However, there is still a demand for downsizing the area of the memory cell.
To meet the demand, therefore, there have been proposed several methods, such as a trench type or a stack type capacitor, which is arranged three-dimensionally in a memory device to reduce the cell area available to the capacitor. However, the process of manufacturing three-dimensionally arranged capacitor is a long and tedious one and consequently involves high manufacturing cost. Therefore, there is a strong demand for a new memory device that can reduce the cell area with securing a requisite volume of information without requiring complex manufacturing steps.
In attempt to meet the demand, there have been proposed a ferroelectric random access memory (FeRAM) where a capacitor thin film with ferroelectric properties such as lead zirconate titanate (PZT) is used for a capacitor thin film.
However, the conventional PZT has several shortcomings for use in the FeRAM. One of the major difficulties of the PZT is that it has the concentration of mobile species such as transition metal ions and Pb vacancies due to the volatility of PbO. In this results, this phenomena causes leakage currents to rise in the PZT.
It is, therefore, an object of the present invention to provide a semiconductor device incorporating a ferroelectric capacitor therein, wherein the ferroelectric capacitor includes Nb doped lead zirconate titanate (PNZT).
It is another object of the present invention to provide a method for manufacturing a semiconductor device incorporating therein a ferroelectric capacitor with PNZT.
It is still another object of the present invention to provide a method for preparing a sol-gel coating solution of PNZT for use in a ferroelectric random access memory (FeRAM).
In accordance with one aspect of the present invention, there is provided a semiconductor device for use in a memory cell, comprising: an active matrix provided with a semiconductor substrate, a transistor formed on the semiconductor substrate, an isolation region for isolating the transistor and an insulating layer formed on top of the transistor and the isolation region; and a capacitor structure, formed on top of the insulating layer, composed of a bottom electrode, a capacitor thin film placed on top of the bottom electrode and a top electrode formed on top of the capacitor thin film, wherein the capacitor thin film is made of Nb doped lead zirconate titanate (PNZT).
In accordance with another aspect of the present invention, there is provided a method for manufacturing a semiconductor device for use in a memory cell, the method comprising the steps of: a) preparing an active matrix provided with a transistor and an insulating layer formed around the transistor; b) forming a capacitor structure on top of the insulating layer, wherein the capacitor structure includes a capacitor thin film made of PNZT; and c) forming a first metal layer and patterning a first metal layer into a predetermined configuration to electrically connect the transistor to the capacitor structure.
In accordance with still another aspect of the present invention, there is provided a method for forming a sol-gel coating solution to make a ferroelectric material, the method comprising the steps of: a) preparing precursors P1, P2, P3 and P4; b) dehydrating the P1 in vacuum and dissolving the vacuum dehydrated P1 in 2-methoxyethanol; c) mixing the dissolved P1 and the P2 under inert gas atmosphere, thereby obtaining a Pbxe2x80x94Nb solution; d) mixing the P3 and the P4 under inert gas atmosphere, thereby obtaining a Zrxe2x80x94Pb solution; e) refluxing the Pbxe2x80x94Nb solution and the Zrxe2x80x94Pb solution; f) adding NH4OH for base-catalyzed condition; and g) adding ethylene glycol as a kind of dry control chemical additive, thereby obtaining the sol-gel coating solution.